1. Field
This disclosure relates generally to semiconductor devices, and more specifically, to source/drain stressors formed using in-situ epitaxial growth.
2. Related Art
To obtain high channel strain from source/drain stressors, the source/drain stressors should be incorporated as close as possible to the channel. When source/drain stressors are grown epitaxially in recesses adjacent to the gate, the recesses require a hydrofluoric acid clean (HF clean) prior to the growth of the source/drain stressors. The materials used for HF clean can, however, attack the gate oxide. To prevent the negative effect of HF clean on gate oxide, the source/drain stressors must be formed at some distance from the channel. Separation between the source/drain region and the channel region creates high series resistance.
Conventionally, the high series resistance in the source/drain region has been reduced by implanting dopants in the source/drain region and annealing the region. Implanting of dopants into source/drain regions can cause other problems. For example, implantation of dopants can cause the stressor layers to relax. The relaxed stressor layers create lower strain in the channel region and thus are not as effective. Additionally, both implantation and annealing can result in a less abrupt change in doping profile from the channel region to the source/drain regions.
Accordingly, there is a need for source/drain regions that stress the channel region and that are formed using in-situ doped epitaxial growth.